1ca1

Background
Alpha toxin is the first bacterial toxin whose enzymatic activity was discovered in 1940 (Songer, JG, 1996; Titball, RW, 1993, Naylor, CE et al., 1998). It is a lecithinase (or phospholipase C) and a sphyngomyelinase hydrolyzing phosphatydil-choline, lecithin, phospholipids and sphyngomyelin (Popoff, MR, 2004; Billington, SJ et al., 1998, Lefevre, PC et al, 2003; Smith, BP, 1996; Titball, RW et al., 1999; Hirsh, DC et al. , 2004). It possesses hemolytic, necrotizing and lethal activities (Titball, RW et al., 1999, Hirsh, DC et al., 2004). Alpha toxin is secreted by all types of Clostridium perfringens and is synthesized in the exponential growth phase (Smith, BP, 1996, Songer, JG, 1996; Titball, RW et al., 1999). Alpha toxin is a protein of molecular weight 43 kDa (Petit, L et al. , 1999). Its synthesis starts from a precursor comprising a signal peptide (the first 28 amino acids). The mature protein is composed of 370 amino acids and comprises two domains: the N-terminal domain is entirely alpha-helical (residues 1-246, the active portion of the toxin), while the other, C-terminal domain is made up of two beta sheets (residues 256-370, involved in membrane binding (Popoff, MR, 2005)). It is a metallo enzyme that binds Zn2+ and Ca2+ ions (Naylor, CE et al., 1998). These ions are essential for biological activity: the zinc is involved in enzyme activity, and calcium is involved in membrane binding (Titball, RW et al., 1999). The gene that encodes alpha toxin is called cpa (also called plc). It is located on the chromosome, near the origin of replication and initiation (Daube, G et al., 1996; Songer, JG, 1996). Its sequence, constant in all identified strains, thus enables its use as a genetic marker of the species (Petit, L et al., 1999). The role of alpha toxin is the destabilization of cell membranes. The diacylglycerol, produced by the hydrolysis of lecithin by alpha toxin, activates protein kinase leading to activation of phospholipases C and D of eukaryotic cells and to a cascade of reactions caused by arachidonic acid. The phospholipases C and D from eukariotic cells provoke the synthesis and attraction of inflammation molecules such as leukotrienes, thromboxanes and platelet activation factors. These reactions lead to the contraction of blood vessels, an increase in the permeability, platelet aggregation, and muscle dysfunction (that of the myocardium in particular). The biological activity of alpha toxin results in membrane lysis of target cells such as leukocytes and enterocytes (Lefevre, PC et al., 2003; Petit, L et al, 1999, Smith, BP, 1996, Minor, L & Veron, M, 1989). Experiments have shown the pathogenic effects by intravenous or intra-peritoneal injection of this toxin (Bunting, M et al., 1997; Titball, RW et al., 1999). Alpha toxin has hemolytic action. This action sets it apart from phospholipase A, whose hemolytic action takes place starting from hemolytic products (Minor & Véron, 1989). However, these products take part in the activation of multiple reactions that alter cell metabolism, leading to cell destabilization (Bunting, M et al., 1997). Alpha toxin alters the permeability of the endothelium and causes the necrosis of intestinal villi (Smith, BP, 1996). Studies carried out by Songer suggest that the tiny differences in the amino-acid sequence of alpha toxin, for gangrenous toxi-infections and for enterotoxemia, confers alpha toxin special resistance to chymotrypsin allowing its accumulation in the intestine (Songer, JG, 1996).

About this Structure
1CA1 is a 1 chain structure of sequence from Clostridium perfringens. Full crystallographic information is available from OCA.